The human eye includes an anterior chamber between the cornea and iris, a posterior chamber, defined by a capsular bag, containing a crystalline lens enclosed by a clear capsule, a vitreous chamber behind the lens containing the vitreous humor, and a retina at the rear of this chamber. The human eye has a natural accommodation ability. The constriction or contraction and relaxation of the ciliary muscle provides the eye with near and distant vision, respectively. This ciliary muscle action shapes the natural crystalline lens to the appropriate optical configuration for focussing light rays entering the eye on the retina. The removal of the natural lens leaves the eye with no means to focus at different distances and necessitates the use of bifocal lenses for near and far work.
Many different IOL designs have been developed over the years and proven successful in phakic and aphakic eyes. IOL implants have been used for years in aphakic eyes as replacements for diseased natural crystalline lenses that have been surgically removed from the eyes. IOLs for aphakic eyes are now implanted after cataract surgery in over 98% of the cases. Visual acuity deficiencies remaining after cataract surgery such as myopia (nearsightedness), hyperopia (farsightedness), and presbyopia (age-related farsightedness) are typically corrected with eyeglasses or contact lenses, though the accuracy of IOL power calcaulation has decreased the need for full-time postoperative spectacle use. The use of surgically implanted phakic IOLs as a permanent form of refractive correction has been gaining in popularity as well, though they are still considered investigational.
IOLs are generally of a fixed focal length. Fused bifocal and aspheric lenses have two or more optical focal planes that are engaged by changing the relationship of the light path or the observer to the lens. All such lenses require movement of either the lens (not possible with a standard IOL), light path, or observer to engage a different focal plane and can therefore be difficult to use. They also have an adverse effect on contrast sensitivity and can cause glare, halos, double vision (polyopia), and other optical aberration all of which compromises visual quality.
Accordingly, there is a need for a multifocal intraocular lens having a variable power of refraction that does not require deliberate engagement of different focal planes for near and far vision.